(1) Field of Invention
The present invention relates generally to an accumulator system for delivery of pressurized hydraulic fluid pressure to blowout preventers (BOPs) and other well equipment during coiled tubing and wirelining operations supporting mineral exploration and production. In drilling and/or work over operations, after a well has been drilled, a cabling apparatus, referred to as wireline, is used to lower various equipment and tools downhole to monitor the conditions in the well and assist in well servicing, intervention, pipe recovery and other operations. A very long metal pipe, referred to as coiled tubing, is also used for well interventions, and is often used to carry out operations similar to wirelining. During downhole operations, it is sometimes desirable to create a seal about the wireline or coiled tubing to allow for maintenance or to mitigate emergency situations. A mechanical apparatus, referred to as a blowout preventer (BOP), is used to seal the wireline or coiled tubing and prevent a blowout. A BOP requires a significant power source, and is typically operated hydraulically to quickly seal the wireline or coiled tubing and close off the well. Hydraulic fluid power is supplied to the BOP by fluidly coupling the BOP to an accumulator system that is capable of delivering the hydraulic fluid power necessary to operate the BOP. In offshore settings, such accumulator systems are usually staged on a tension-leg platform, production module, stationary platform, inland barge, jack up boat, lift boat or other elevated vessel. In workover operations, such accumulator systems are staged as close to the well head as practical.
Presently, coiled tubing and wireline blowout preventers are operated by accumulator systems that generally operate with less hydraulic fluid than the capacity of the accumulators. This problem stems from the need for such accumulator systems to have a small size or footprint for operation from a tension-leg platform, production module, stationary platform, inland barge, pro, jack up boat, lift boat or other elevated vessel. Likewise, workover operations require an accumulator system with a small size or footprint for use in close proximity to the well head. Such accumulator systems pose several problems. First, any leak or other casualty resulting in the egress of hydraulic fluid from the accumulator system renders the system inoperable. In such a scenario, the operator must either connect a different accumulator system to the BOP or attempt to correct the leak or other condition that resulted in the egress of hydraulic fluid from the system. Both alternatives expend considerable time and may result in the failure to mitigate an emergency situation. Second, a leak or other casualty resulting in the spill of hydraulic fluid that occurs after the closing of a BOP may render the accumulator system unable to hold the BOP in the closed position. Third, a limited hydraulic fluid capacity limits the number of BOPs or other well equipment that can be simultaneously operated by the accumulator system. Thus, exploration and production, activities that involve the simultaneous operation of several BOPs or other well equipment often require the use of more than one accumulator system.
Additionally, accumulator systems for use in wirelining and coiled tubing operations offer little in the way of redundancy, often comprising one electrically or pneumatically operated pump and a hand pump. This problem also stems from the need for such accumulators to have a small size or footprint for operation from a jack up boat, lift boat or other elevated vessel. The hand pump is used in the event that the electrically or pneumatically operated pump is inoperable. Pressurizing a hydraulic system for use in well operations with a hand pump is time consuming and impractical. Moreover, a single pump coupled with a hydraulic fluid capacity that is less than the capacity of the accumulators results in an accumulator system that is slow to charge to a pressure necessary to operate the BOP.
(2) Background Art
There are several accumulator systems and other systems for providing pressurized hydraulic fluid for the operation of subsea well equipment. Examples of such systems include, but are not limited to, U.S. Pat. App. Nos. US2012/0279720, US2015/9004175, and US2013/8602109. While such systems fulfill their particular purposes, they do not address the need for a redundant accumulator system with a small footprint that can quickly be charged to operational pressure and that has sufficient hydraulic fluid capacity to overcome hydraulic fluid leaks and operate a plurality of BOPS or other well equipment.